By far most of the wafers produced today are provided with chips or so-called dices only on one side. Wafers are equipped in mass production and at the same time there is the requirement of the industry to implement smaller and smaller structures. This also applies to the thickness of the wafer, especially for multilayer wafers which are repeatedly stacked.
The further optimum use of the available space leads to wafers being required which are provided with chips or dices which are more and more double-sided recently, therefore on both sides, and through silicon vias (TSVs) can enable electrical contacts between the front and back of the product wafer.
The greatest problem in the production of these double-sided wafers consists in handling during mass production, which can comprise different production steps, such as for example bonding, debonding, alignment, grinding, etching and many others. Stabilization of the large-area product wafer which generally has a diameter of 300 mm by a carrier wafer is necessary especially due to the thinning/back thinning of the product wafer which is provided in the production process.
Stabilization or support by a carrier wafer in wafers outfitted on one side is therefore comparatively simple since the carrier wafer can be temporarily bonded on the side facing away from the side provided with chips. But here process steps can be necessary on the front and back as well.
Generally, in temporary bonding there is the problem of detaching the product wafer which is passing through the different production steps from the carrier wafer carefully and nondestructively after completion of these production steps. The connection between the carrier wafer and the product wafer therefore during use of different production steps must be strong enough to hold and stabilize the product wafer. At the same time the connection should however then be easily and quickly detachable.
WO 2009/0945558 A2 describes a temporary bonding method for a product wafer which is outfitted on one side.
The generic methods accordingly have in common that each product wafer in the production process must be exposed to at least one process step on each side. The product wafers are processed nowadays, for reasons of easier handling, first at their initial thickness, therefore before back-thinning, on their first side, for example the production of bumps or groups of bumps. Then the product wafer is bonded onto a carrier in order to be able to thereupon subject the product wafer to the process step of back-thinning. After back-thinning generally other process steps are then carried out on the second side, for example in turn the production of bumps and/or groups of bumps and/or other interconnection layers and/or the application of chips. To the extent after processing the second side one process step is again necessary on the first side of the product wafer, in the prior art there is the major problem that the thinned and very sensitive product wafer which has already been provided in part with expensive chips must be detached from the carrier in order to make the first side accessible to further process steps.
The object of this invention is to devise a method for producing a product wafer which is provided with chips especially on two sides, by which the product wafer can be reliably and carefully handled during the production process.